Although the most common bacteria in the supragingival plaque are Gram-positive streptococci, no extensive investigations have been conducted into the susceptibility of these species to chlorhexidine and cetylpyridinium chloride. Therefore, in this study, we investigated the susceptibility of 80 streptococcal strains in planktonic or biofilm states to these two antimicrobial agents. The minimum inhibitory concentration MIC and minimum bactericidal concentration MBC of the planktonic streptococci were measured using the microdilution method, as were the minimum biofilm inhibitory concentration MBIC and minimum biofilm eradication concentration MBEC measured on streptococcal biofilms formed on 96-well plates. In all species, the MIC, MBC, MBIC, and MBEC values were higher for chlorhexidine than for cetylpyridinium chloride, with sensitivity values varying according to species. For chlorhexidine, the MIC, MBC, and MBIC values showed statistically significant differences among species. However, only MBEC values showed statistically significant differences for cetylpyridinium chloride. The MIC against Streptococcus mutans and the MBC against Streptococcus salivarius were significantly lower than those against the other species. With the exception of a few species, most of the bacterium susceptibility values were higher in the biofilm state than in the planktonic state.
In this study, an automated sensor to measure forest fire surface fuel moistures was developed to predict changes in the moisture content and risk of forest fire surface fuel, which was indicators of forest fire occurrence and spread risk. This measurement sensor was a method of automatically calculating the moisture content of forest fire surface fuel by electric resistance. The proxy of forest fire surface fuel used in this sensor is pine (50 cm long, 1.5 cm in diameter), and the relationship between moisture content and electrical resistance, R(R:Electrical resistance) =2E(E:Exponent of 10)+13X(X:Moisture content)-9.705(R 2 =0.947) was developed. In addition, using this, the software and case of the automated measurement sensor for forest fire surface fuel moisture were designed to produce a prototype, and the suitability (R 2 =0.824) was confirmed by performing field monitoring verification in the forest. The results of this study would contribute to develop technologies that can predict the occurrence, spread and intensity of forest fires, and are expected to be used as basic data for advanced forest fire risk forecasting technologies.
This study examines the risk of spontaneous combustion caused by the residue of the coin plating experiment. In this study, three cases of recent fires due to the unauthorized disposal of the residues left from coin plating experiments in middle and high schools of the Gangwon-do Province (2017~2018) were analyzed and an experiment to recreate the fire was conducted. As a result of the analysis of the three cases of school fires, it was shown that the students who participated in the coin plating experiment wiped the aqueous solution that spilled onto the table during the procedure as well as the residue of the solution inside the beaker with a tissue and disposed of it on the classroom floor or in a plastic trash can along with the coin that was used. If short, 1 h and 18 min, if long, 8 h and 15 min after the tissues with the residues were thrown away in the trash can, a fire broke out. In addition, when the fire experiment was recreated, in a state where 5 g of sodium hydroxide and 5 g of powdered zinc were partially overlapped, 0.25 ml of water was added. After 20 min since the start of the experiment, a fire occurred as the temperature rose to 549 ℃. In particular, when the coin experiment residue was put on toilet paper and dried for 5 min using a hair dryer, a fire occurred as flames started to appear from the residue. Therefore, in order to prevent fires, it is safe to dispose of the residues after conducting the coin plating experiments in waste incinerator machines. Fire safety education must also be enforced upon teachers who are in charge of instructing chemical experiments at school, and science laboratories must be equipped with automatic fire extinguishing facilities, e.g., trash cans that are placed in the classrooms must be made of steel to ensure complete safety.
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